I. Field of the Invention
This invention relates to a method and apparatus for surveilling articles and in particular to improvements in a method and apparatus for detecting or preventing the theft of articles and more particularly it concerns the method and apparatus capable of distinguishing labels from all other objects within an oscillating electromagnetic field and a new type of label with a recognizably different signature from all other ferromagnetic labels.
II. Description of the Prior Art
In the art of antishoplifting machinery and labeling, the most successful developments have been those which correspond with labels carrying a code capable of being electromagnetically altered to designate the labeled article as being sold or checked out. Illustrative of this in the commercially available systems is the labeling and detecting arrangement offered to libraries by Minnesota Mining and Manufacturing Company (3M) under the trademark Tattletape. This group of devices includes a plurality of patents by Edward R. Fearon and one by Robert E. Fearson.
U.S. Pat. Nos. 3,631,442; 3,747,086; 3,754,226; 3,790,945 and 3,820,103 are illustrative of the antishoplifting machinery and labeling systems which illustrate a number of alternate proposals and shall serve as background for this particular invention.